Indian Journal of Fibre & Textile Research Vol. 37, March 2012, pp. 74-82 Development of a quantitative assessment method for self cleaning by photocatalytic degradation of stains on cotton Bhavana Sharma, Manjeet Jassal a & Ashwini K Agrawal a SMITA Research Labs, Department of Textile Technology, Indian Institute of Technology, New Delhi 110 016, India and Nidhi Goyal & Deepali Rastogi Department of Fabric and Apparel Science, Lady Irwin College, University of Delhi, Delhi 110 001, India Received 27 October 2010; revised received and accepted 13 April 2011 This paper reports a standardised method termed as Stain Degradation Assessment (SDA) method, developed for the quantitative evaluation of self-cleaning efficiency of the finished fabric. The method involves (i) a standardized staining procedure to apply a uniform stain on the fabric, (ii) instrumental evaluation of photodegradation of stain in terms of K/S using a template to reduce error, and (iii) analysis of K/S values to evaluate stain degradation in percentage and its comparison with visual assessment. This method has been found to give a reproducible and comparable assessment of stain degradation on the textile material with respect to UV exposure. Keywords: Cotton, K/S coefficient, Self-cleaning activity, Stain removal, Template, Titania, UV irradiation 1 Introduction Nanocrystalline titanium dioxide or titania (TiO 2 ) has emerged as the most interesting and promising photocatalytic material and its coatings have been used in various applications, viz. water purification, air purification, sterilization/disinfection and self-cleaning materials 1-10 . The photocatalytic activity of titania depends on its crystalline phase and particle size. Among the different crystalline phases of titania, anatase is recognized as the most active and shows the best photocatalytic activity, in comparison with other phases (rutile and brookite), because of its wide energy band gap (3.23 ev) corresponding to radiation in near UV range. The detailed mechanisms of the self-cleaning processes that occur on titania surfaces have been thoroughly investigated over the past decade 11-13 . Briefly, in photocatalytic reaction, photogenerated electron and holes migrate to the semiconductor surface where they can induce reduction and oxidation of absorbed molecule, such as any pollutant or stain. The quantitative assessment of photocatalytic activity of titania is primarily carried out in the aqueous suspension/sol using a dye. Some of the dyes that are being used for the assessment are solophenyl green 14 , methylene blue 15 , rhodamine B 15 , basic red 16 and acid yellow 17 . In this method, a known amount of dye is added in the titania suspension and degradation of colour is assessed by UV-Vis spectrometry after various time intervals of UV exposure. In another method, the photocatalytic assessment of titania treated cotton fabric was studied by immersing the fabric in the dye solution followed by exposure to UV irradiation. The decomposition of colorant was then assessed spectrophotometrically by analyzing the decrease in concentration of the colorant in the solution 9 . These assessment methods of decomposition of dye are being used for the removal of dye from water and wastewater treatment. Though these methods can provide relative activity of the catalyst particles, they are unlikely to give correct assessment of self cleaning behaviour of a finished fabric in a real situation. This is because the kinetics of degradation of a dry stain on a dry fabric is likely to be different from the kinetics of degradation of dye in solution form with wet catalyst. In dry state, the interaction of the dye and catalyst may depend upon their relative position on and inside the fabric. The photocatalytic self-cleaning action of nanocrystalline titania on textile through degradation of various categories of stains such as coffee, wine, perspiration on textile surface has been studied by several researchers. Evaluation method of stain ________________ a To whom all the correspondence should be addressed. E-mail: manjeet.jassal@smita-iitd.com; ashwini@smita-iitd.com